Mexico got their World Cup campaign off to a perfect start with a 1-0 win over Cameroon -- but again the officials took much of the limelight.

The winner came just after the hour through Oribe Peralta, Mexico's top-scorer in qualifying, who pounced on the loose ball after Charles Itandje had saved well from Giovani dos Santos to slot into the empty net.

But Mexico should already have been well in control of the match, with Dos Santos having two goals wrongly ruled out for offside before the break. Replays showed he was behind the last defender when latching onto a cross to fire home. And then he was adjudged offside from a corner when the ball had flicked off the head of a Cameroon player.

"We could have scored more, but unfortunately we're not used to these conditions,'' Mexico coach Miguel Herrera said. "Frankly, the refereeing took away two clear goals, but at the end of the day you've got to work for it, and we get to the next match with three points and very high spirits."

Cameroon almost snatched a last-gasp equaliser but Guillermo Ochoa saved well from a firm Benjamin Moukandjo header.

Mexico join Brazil on three points at the top of the group, after the hosts beat Croatia 3-1 in the curtain-raiser on Thursday in which the referee came in for much criticism.

Both Mexico and Cameroon had entered the competition with question marks over their readiness.

Mexico -- having had four coaches in the past year and only qualifying via a playoff against New Zealand -- boasted little form having lost recent friendlies to Bosnia-Herzegovina and Portugal.

And Cameroon's preparations had been chaotic with the squad arriving in Brazil a day later than planned after a row over bonuses with their national federation. The African players had also been under fire from their fans and media after failing to accept a symbolic flag from their prime minister.

Those issues seemed to be hampering Cameroon as they started poorly and rarely threatened to improve upon a record that has seen them win just once at a World Cup finals since 1990.

Mexico quickly made an impression with Miguel Layun firing over and Hector Herrera shooting at former Liverpool goalkeeper Itandje from distance.

The first moment of controversy came when Dos Santos brilliantly turned in a cross from Herrera on the volley only to see a flag raised. Replays suggested the striker had been unlucky, although it was a marginal call.

Eric Choupo-Moting put the ball in the net as Cameroon finally started to show some life, but there was little doubt about the offside decision that denied him.

In a good spell for Cameroon, Tottenham's Benoit Assou-Ekotto charged down the left to tee up Samuel Eto'o but the Chelsea forward's shot grazed the post.

Choupo-Moting was unlucky again when he headed straight at Ochoa and Mexico eventually scrambled clear.

Cameroon's purple patch proved brief and Mexico were denied by a flag again when Dos Santos stooped to head in from a Layun corner. The ball was diverted into his path by Choupo-Moting and not flicked on by a Mexico teammate, leading to more furious appeals from the El Tri players.

The first half ended with Stephane Mbia escaping a booking for connecting with a forearm to the head of Alex Song. It was one of a number of robust challenges which Roldan dealt with leniently.

Mexico maintained their tempo after the break and Peralta was denied by a good Itanjde block.

Cameroon's next chance came from a set-piece as Assou-Ekotto had a free-kick deflected narrowly wide.

Mexico deservedly made their breakthrough just after the hour. Dos Santos raced through but was denied again, this time by Itanjde, but Peralta seized on the rebound to stroke the ball home.

"I want to score as many goals as possible," Peralta said, "to take advantage of every opportunity that I get because I want to be a world champion again.''

Peralta made way for Hernandez soon after as Mexico looked to his fresh legs to make the win secure.

Cameroon also made a forward change as they searched for an equaliser, sending on striker Pierre Webo for former Arsenal midfielder Song.

Rafael Marquez blocked a shot from Choupo-Moting and Francisco Rodriquez needed to stretch to intercept as Eto'o threatened.

Ochoa then did well to keep out Moukandjo's header but Hernandez should have made it 2-0 when he missed the target in injury time.

The loss leaves Cameroon needing a victory over group rival Croatia before closing first-round play against Brazil.

"We have five days to recover,'' Cameroon coach Volker Finke said. "We will analyse this together because the match against Croatia is very important if we want to stay alive."